This invention relates to an apparatus and method for cutting of sheets of soft flexible foam material into cylindrical type rods suitable for use in joint backing application. In particular, the invention relates to apparatus and method for cutting of soft flexible polymeric foam slabs to form long continuous lengths of cylindrical backing rods from the thickness of the foam as the slab is progressively moved past a cutting operation.
Cutting of soft flexible polymeric foam has proven difficult and attempts to extrude such foam into a particular shape have also proven unsatisfactory as a dense skin occurs. One method of forming particular shapes from foam slab is disclosed in U.S. Pat. No. 3,869,831, where shaper rollers grind the exterior surface of the foam to produce the particular shape. According to this patent, first one surface of the foam slab is shaped and then the foam is passed to a second station which does a similar operation to the opposite side. This apparatus has operated satisfactory, however it requires two separate cutting operations which must be controlled and aligned to assure the desired shape is achieved. It also results in substantial amounts of fine scrap as the surface has been ground.
It is also known from U.S. Pat. No. 3,009,848, to compress the sheet or block of soft plastic foam and cut it in a particular manner often with straight knives which upon release of the foam results in a particular shape being achieved which is different from the cutting knife. In this way, straight knives can be used which are obviously much simpler to control relative to specially shaped knives.
Other methods for producing cylindrical rods from block foam have used a long hot wire which is inserted in the foam and moved in a manner to cut the rod from the foam block. This is a batch process operation and results in fairly high manufacturing costs.
The cutting of soft flexible open cell polymeric foam remains a problem particularly due to the foam's resilent compression and elastic deformation resulting at least partially from the low density and causes shifting of the foam during cutting thereof. However, when the foam block or slab is properly guided and of sufficient thickness, it is fairly firm and it is only when much smaller widths of the foam are cut that it becomes fairly flexible. Therefore, the foam blocks or slabs have somewhat different characteristics than the individual cylindrical rods cut from the slab, caused by the reduced size.